This invention relates to probes or detectors for corrosion resistant vessels. Historically it has been difficult to provide access for detectors or probes into corrosion resistant vessels including tanks and conduits, especially when such vessels are lined with a contiguous, often brittle, material such as glass or ceramic. This is true for several reasons. It is difficult to provide small access holes through a glass or ceramic lining since such holes provide stress points which are often subject to failure. Furthermore, even after such an access hole is provided it is difficult to provide a reliable seal around the detector or probe which passes through the access hole. This is especially true since such seals are often required to be corrosion, pressure, heat and electrically resistant Such seals are usually made from a corrosion resistant thermoplastic material such as polytetrafluoroethylene, commonly sold under the trademark TEFLON. The reliability of the seal is therefore dependent upon the properties of the sealing material, the sealing surface and pressure applicable to the seal.
Numerous attempts have been made to overcome these problems but all of them require complex sealing mechanisms are unreliable or both. One such example is shown in U.S. Pat. No. 4,200,834, incorporated herein by reference. This patent illustrates problems associated with providing access to glass lined vessels by probes or detectors. In that patent the access is not only complex, but provides very little sealing surface area to prevent failure, e.g. gasket 31 or seal 19. Another complex construction is shown in U.S. Pat. No. 4,595,487, incorporated herein by reference. In that patent a small access hole is provided which is surrounded by a flange 15. The short bends around such a small hole result in stress points which subject a glass lining to failure. In addition sealing gasket 21 has very little sealing surface area which creates potential for gasket failure. U.S. Pat. No. 4,617,511, incorporated herein by reference, shows an electrode for introduction into a glass lined vessel. The assembly has a protruding electrode 1 sealed by means of a small gasket 7.
A unique and interesting approach to the problem is presented in Data Sheet DS33-101-2, Fault Finder System 125 of Pfaudler U.S., Inc., August 1991. The probe illustrated in FIG. 3 of that data sheet is essentially shown in FIG. 3 herein as prior art. This prior art probe has a ring having a glass coating 40 having sealing surfaces 44 for mating with flange surfaces of a vessel with intervening sealing gaskets. A probe 10 passes through the body to a central hole 18 of the ring. The probe is recessed to permit the area of a full circle within the central hole to permit full access through the central hole to a vessel. As a result surface area 44 has a restricted area 46 which is a weak area for holding a sealing gasket. In addition probe 10 is sealed within access hole 22 by means of Teflon ring seal 42. The probe relies upon this ring seal for both resistance to the contents and conditions within the vessel and electrical resistance to isolate the probe. The small nature of ring seal 42, the small sealing surface area and the difficulty of applying positive pressure to retain the ring seal, make the ring seal subject to more failures than are desirable.